A 7.5-μW 0.08-mm2 single-ended SC delta-sigma ADC for acoustic sensor applications

This study presents an ultra-low-power, small-size, 1-bit, single-ended, and switched-capacitor (SC) delta-sigma analog-to-digital converter (ADC) for wireless acoustic sensor nodes. This wireless sensor node has a delta-sigma ADC that converts the sensed signal to a digital signal for convenient data processing and emphasizes the features of small size and low-power consumption. The chip area of the delta-sigma ADC is dominated by the capacitor; therefore, a novel common-mode (CM) controlling technique with only transistors is proposed. This ADC achieves an extremely small size of 0.08mm(2) in a 130-nm CMOS process. The conventional operational transconductance amplifiers (OTAs) are replaced by inverters in the weak inversion region to achieve high power efficiency. At 4-MHz sampling frequency and 0.7-V power supply voltage, the delta-sigma ADC achieves a 55.8-dB signal-to-noise-plus-distortion ratio (SNDR) and a 298-fJ/step figure-of-merit (FOM) in a signal bandwidth of 25kHz, while consuming only 7.5W of power. Copyright (c) 2015 John Wiley & Sons, Ltd.